Icahn and Ackman even had a famous (for financial nerds at least) argument on CNBC about Herbalife in 2013.

The two traded personal barbs, with Ackman saying that "Carl Icahn unfortunately does not have a good reputation for being a handshake guy" and Icahn telling Ackman "I wouldn't invest with you if you were the last man on Earth!"

Ackman and Icahn buried the hatchet a year later, with both men agreeing to let bygones be bygones during an investment conference in 2014.

But their battle about Herbalife wound up becoming the subject of a 2016 documentary called "Betting on Zero."

To the chagrin of Ackman and delight of Icahn and anyone else who took the opposite side of Ackman's trade, it seems "Betting on $100" may be a more apt title given Herbalife's current price.